1. Field of the Invention
The present invention relates generally to a system and method for providing streaming content to a requester and more specifically to streaming content from a stream engine node to a requester while meeting Quality of Service constraints.
2. Description of the Related Art
Digital streaming data, which includes continuous media such as audio and video streams, must be delivered in a predictable way from source to destination in order to preserve and reproduce at the destination the timing relationships that existed at the source. This generally means delivering packets making up the stream in order and on time. Failure to do so causes garbled and unusable results at the destination. One way of reliably delivering the packets that make up digital streaming data is under a Quality of Service constraint.
Quality of Service (QoS) constraints are well known in the area of networking. For example, a QoS constraint on the transport service of a network can require that a transport connection be established within a specified period of time, that a certain level of throughput be maintained by the established connection over a specified time interval, and that the transport layer provide protection against unauthorized third parties accessing transported data. These constraints can be requested by the user when establishing the connection at the transport level. Very often, if the transport layer cannot achieve the requested constraints, a negotiation occurs between the requesting site and the remote sites of the connection for a set of constraints that are acceptable to both ends of the connection. If a set of constraints is found to be acceptable to both ends of the connection, the connection is set up and the constraints are maintained throughout the duration of the connection.
Though difficult, meeting reasonable QoS constraints in the network context is achievable because the times involved are on the order of microseconds. However, a storage system that is connected to a network meeting QoS constraints is another matter. Storage systems that provide streaming data operate with times on the order of milliseconds and, if rotating media are involved, may have unpredictable response times and throughputs. Streaming data includes an audio stream or video stream or other continuous media for which the receiver must reproduce the timing relationship that existed at the transmitter. The delivery of such data benefits from traversing a network having QoS constraints.
For a network that is connected to such storage systems, it does little good for streaming to have the network meet the QoS constraints while the storage system does not. The servicing of a streaming request by such a storage system will appear to the user as unpredictable and slow and possibly unworkable if the stream is being viewed in real time, even though the network is performing adequately under its QoS constraints. One such prior art streaming storage system 100 is shown in FIG. 1.
In FIG. 1, a plurality of intelligent storage managers 101 each control a plurality of disk or tape devices 102. These intelligent storage managers are connected to one or more servers 103 via a first set of switches 104. The servers in turn are connected to routers 105 for access to the outside world via a second set of switches 106. When a streaming request 107 is made of the system, the request 107 passes through the router 105 and second set of switches 106 to one of the servers 103, which then accesses one of the storage nodes 102 on which the requested streaming object is located. The requested data 108 is then delivered to the server 103 servicing the request, and that server 103 then delivers the requested data to a switch 106 in the second set, to the router 105 and then to the outside world where the requester is located.
Such a system configuration makes it difficult, if not impossible, to meet a QoS constraint on the response time and throughput in servicing the streaming request. The reason is that the requested data must flow through the server 103 system. Thus, a QoS constraint or guarantee can only go so far as the routers 105 and the second set of switches 106, as shown. Prior art systems have sought to remedy this problem by providing more processors and memory in the servers, in effect over-provisioning the servers. However, this solution is expensive, wastes resources, and is not scalable, in the sense that the system cannot grow easily to handle more concurrent streaming requests.
Therefore, there is a need for a storage system, especially a storage system that supplies streaming data to provide the data under the QoS constraints just as the network does, in a scalable manner and without requiring excess resources.